Answer
The increase in the thermal energy of his body and the ground along which he slides is $~~3500~J$
Work Step by Step
We can find the initial kinetic energy of the baseball player:
$K = \frac{1}{2}mv^2$
$K = \frac{1}{2}(70~kg)(10~m/s)^2$
$K = 3500~J$
Since the player slides to a stop, the decrease in the player's kinetic energy is $~~-3500~J$
By conservation of energy, the increase in the thermal energy of his body and the ground along which he slides is $~~3500~J$
